Field of the Invention
The invention generally relates to a dampener lubricator for a plunger lift system.
Description of the Related Art
To obtain hydrocarbon fluid from an earth formation, a wellbore is drilled into the earth to intersect an area of interest, such as a hydrocarbon-bearing reservoir, within a formation. The wellbore may then be “completed” by inserting casing within the wellbore and setting the casing therein using cement. In the alternative, the wellbore may remain uncased (an “open hole wellbore”), or may become only partially cased. Regardless of the form of the wellbore, production tubing is typically run into the wellbore (within the casing when the well is at least partially cased) primarily to convey production fluid (e.g., hydrocarbon fluid, which may also include water) from the reservoir within the wellbore to the surface of the wellbore.
Often, pressure within the wellbore is insufficient to cause the production fluid to naturally rise through the production tubing to the surface of the wellbore. Thus, to carry the production fluid from the reservoir within the wellbore to the surface of the wellbore, an artificial lift system is sometimes necessary. Some wells are equipped with a plunger lift system to artificially lift production fluid to the surface of the wellbore.
A plunger lift system generally includes a piston, often termed a “plunger,” which cyclically travels the length of the production tubing. The plunger acts as a free piston to provide a mechanical interface between lifted gas from the formation disposed below the plunger and the produced fluid disposed above the plunger, thus increasing the lifting efficiency of the well.
Once the fluid is lifted by the plunger, it flows upward through the production tubing until it reaches surface equipment. The surface equipment includes a lubricator for absorbing the shock of force exerted by the upwardly-moving plunger at the end of the plunger's up-stroke. During the plunger cycle, the plunger runs within the bore of the production tubing for the full length of the production tubing between a lower bumper spring and the lubricator.
FIG. 1 shows a typical lubricator 100 having an upper end 101 and a lower end 102. The lubricator 100 includes a tubular body having a first tubular section 103, usually termed a “spring housing,” connected to a second tubular section 104. Seals, such as o-rings 105, are provided at the connection point between the tubular sections 103, 104 to prevent fluid communication between a bore 108 of the lubricator 100 and the atmosphere. A cap 130 is connected to an upper end of the spring housing 103.
First and second flow outlets 110, 120 and a catcher assembly 140 extend from the tubular body. The catcher assembly 140 retains the plunger to facilitate inspection of the plunger. Handles 135 also extend from the first tubular section 103 to permit lifting of the lubricator 100. At an upper portion of the tubular body, the lubricator 100 includes an upper bumper spring 109 within the bore 108 to attempt to absorb the shock or kinetic energy of a plunger at the end of a plunger up-stroke. A bumper plate 106, which is disposed within the bore 108 directly below the upper bumper spring 109, provides a solid contact point for the plunger. The bumper plate 106 includes an opening 107 which allows fluid communication between the portions of the bore 108 above and below the bumper plate 106.
Using the bumper spring 109 within the lubricator to absorb the shock of the plunger on the plunger up-stroke is problematic for several reasons. First, the force of impact of the plunger against the spring often causes the bumper spring to fail, break, or become otherwise damaged. Damage to the spring may require replacement of the spring, decreasing the profits of the well because of down-time during spring replacement. Additionally, damage to the spring may decrease the shock absorption ability of the spring, eventually causing the plunger to blow out the cap and exit the lubricator into the atmosphere. Blowing off the cap from the lubricator creates a safety hazard and usually causes damage to the lubricator, also decreasing the profitability of the well due to down-time to replace or repair the lubricator. Additionally, damage to the spring may cause damage to the plunger upon impact with the striker assembly due to ineffective or non-existent cushioning of the plunger. The damaged spring increases operating costs of the well not only because of down-time which occurs to replace or repair the plunger, but also because of the additional cost of replacement parts.
Therefore, there is a need for a lubricator having an improved ability to cushion the plunger at or near the end of the up-stroke of the plunger.